In December, PCWorld posted a major story about the tech amenities available to travelers in America's airports ("20 Best U.S. Airports for Tech Travelers"). In it we focused on the airports themselves, but often airlines are responsible for driving the installation of new tech amenities in gate areas. The airlines know that electrical outlets, work desks, and zippy Wi-Fi can influence passengers' decisions to fly with Airline A or with Airline B.

As a result, some airlines have become deeply involved in making their gate areas a more welcoming place for laptop and smartphone users. Others have focused on developing apps and mobile websites, and offering in-flight Wi-Fi service in their planes. Not surprisingly, some airlines are more progressive than others when it comes to techy stuff. Here's how the U.S. airlines stack up. (See a ranked chart of the top 10 U.S. airlines, comparing their features.)

1. Delta

Delta has upgraded about 20 of the airports where it operates with Delta-branded charging stations. Those stations have made a huge difference in the number of available outlets and USB ports at the gates. And Delta's iPad installations at New York's JFK and LaGuardia airports, and (soon) at Minneapolis-St. Paul International are truly impressive.

Delta's tech focus doesn't stop at the gate. All of its large domestic aircraft now offer Gogo Wi-Fi on board. The carrier is looking for a way to outfit its 250 international aircraft with Wi-Fi, too, since Gogo's ground-based service can't reach beyond 100 miles offshore.

Aside from the usual array of features (flight updates, mobile boarding passes, seat maps, and so on), Delta's Fly Delta mobile app offers capabilities that most other airline apps don't--such as the ability to track your checked bag by scanning your bag tag with your smartphone. User reviews of Fly Delta in app stores are generally positive, though the app does lose a few points for not letting the user book new flights; you can use it only to change existing reservations.

Delta also has the strongest presence of any airline on both Twitter and Facebook. The company allows customers to book travel directly from Facebook, and it offers the @deltaassist hashtag on Twitter for people who encounter support issues. Delta's "social media lab" is peopled by regular customer service reps who watch for Delta customers tweeting about problems or annoyances, and then provide support in real time over Twitter or other channels if necessary.

Delta says that its social networking efforts pay off both financially and in customer loyalty. "We want to engage with our customers with our digital channels as much as possible," says Delta's vice president of e-commerce Bob Kupbens. "We feel it's a great way to improve customer service. It's a way for us to get people out of line and off the phone, which is good for the customer and good for Delta."

2. Alaska

Though Alaska itself doesn't have any branded tech amenities in its terminals, the airline operates in airport terminals that have a high density of outlets and Internet kiosks. The fact that the airline shares many terminals and concourses with Delta (an airline that invests in charging stations at the gates it serves) helps Alaska out a lot. But the airline is tech-conscious itself, as evidenced by its well-maintained and interactive Facebook and Twitter pages. Alaska often reaches out to customers via Twitter; but it also posts new content, which makes following the airline on Twitter worthwhile.

Surprisingly, Alaska Air has a fairly functional app, called the Travel App, that lets you change your seat assignment, add notes about your hotel and car rental, and check into your flight. The app also supports mobile boarding passes at select airports. One drawback is that you can't use the same reservation to check in multiple travelers, so it's not ideal for family use.

Alaska has been the most progressive U.S. airline at making onboard Wi-Fi available. Today, some 92 percent of the planes in Alaska's fleet have Wi-Fi service installed.

3. Virgin America

Virgin America is a tiny airline that beat out largerr rivals in our rankings by keeping its passengers connected while they wait for a flight, and while in-flight.

In about half of the terminals that Virgin services, the outlet densities are higher than the average for the airport as a whole.

All Virgin planes have onboard Wi-Fi, and the company is transitioning from Gogo (ground-based) to a satellite-based service. The size of the company's fleet will reach 57 aircraft in 2013, and all planes will be equipped with this technology. Virgin recently partnered with Google to lend Google Chromebooks to passengers 10 minutes before boarding, so they can take advantage of free Wi-Fi during the flight.

Conversation on Virgin America's Facebook is a bit of a one-way street, as the airline doesn't seem to respond to user's comments in that forum; but overall it scored very well for use of social media.

4. American Airlines

American has a high density of outlets in its terminals, but it doesn't offer much in the way of Internet kiosks, work desks, or other branded amenities. The carrier does, however, respond to Twitter followers who have complaints, so American earned high rankings in our social media scores.

Onboard Wi-Fi is limited to 30 percent of American Airlines flights. However, customers can stream content (such as onboard movies, TV, and music) to their wireless devices while in flight--an especially welcome option given that many American flights don't have seatback monitors.